1. Field of the invention
This invention relates to the removal of dust and lint and also static charge simultaneously from surfaces. In many industries the elimination of particulate materials such as dust and lint is of utmost importance. On plastic and non-conductive surfaces it is also necessary to remove any static charge at the same time as this static charge will bind these particulates to the surface by electrostatic forces as well as attract more such particulate matter to that surface.
An example of the importance of the above is found in the photo-processing industry When positive prints are made from photographic negatives, it is necessary to keep these negatives free from dust and lint so that the dust and lint are not imaged on the prints making them unacceptable. Other examples are industries that fabricate items from sheets of plastic, especially when the plastic is transparent. Picture framing using clear acrylics is a typical application where the dust and lint must be removed before the picture is installed. If the static charge is not removed, it is nearly impossible to remove the dust and lint. Laminating is another similar application. These are a few of the many places where dust, lint and static charge removal is essential.
2. Description of Prior Art
Over the years many methods have been devised to eliminate static charges from plastic surfaces. The primary method is by making the surrounding air electrically conductive, thus allowing the electric charges to be conducted away from the surface. These include such techniques as vaporizers and atomizers to humidify the air, radio-active material to ionize the air, and also high voltage emitters to ionize the air. Other methods which make direct contact with the surface have been used, such as metallic brushes, wipers, and liquids which are applied directly to the surface.
Static charge on non-conductive plastic surfaces usually develops as the result of contact with another plastic item. Such plastic surfaces, or items in contact, have an atomic valence attractive force that holds them together. This force is electric in nature and is of the variety that holds materials together. Separation of the items results in a rending of some of the negatively charged electrons from one of the surfaces by the stronger attractive force of the other, and the adherence of those electrons to that surface. Thus, the surface that has lost electrons is left with an electric charge to again attract negatively charged electrons, and has thereby acquired a positive charge. And, the surface which has gained the surplus of electrons has thereby acquired a negative charge.
This is a classic example of how static charges develop. However, static charges are known to develop in many ways and on surfaces and bodies that do not fit the above example. Static charges are transferable through conductive means such as in a Van de Graff generator, or by accumulation of charge on an electrically isolated body through friction means, such as an aircraft or a car by friction with the passing air. Charges can also be accumulated from direct contact with high voltage sources or by transmission from a surrounding ionized atmosphere.
Except in a vacuum, static charges tend to dissipate or leak off through the conductivity of the surrounding atmosphere. The more conductive the atmosphere, the faster the charge will leak off. In humid weather, the moisture in the air makes the air more conductive than in dry weather when there is little moisture in the air. Thus, we seldom encounter static charge on a humid day and frequently encounter it on a dry day.
Static charges are transferable. Static charge acquired by our clothing is transferred to our body or parts of our body. And, when we approach an object of different electrical potential (usually a ground potential), we experience an electric discharge as electrons arc from our finger to that object, or vice versa. Static charge can also be transferred from our bodies to tools or other items we contact. These tools in turn can impart the charge to a sensitive component causing damage.
Although an in depth discussion of the principles of the many techniques for removing static charge as well as eliminating dust, lint and other particulates can be pursued, let us limit the range of this discussion to the immediate scope as defined by the application of the devices that will emanate from the subject invention.
This invention is concerned with the removal of static charge, dust and lint by the use of a device that incorporates brush-like elements. Brushes have been used since the earliest of times for removing dust and lint. In more recent times they have been augmented by air ionizing means for eliminating static charge Lately the brushes themselves have been fabricated from electrically conductive filaments or by the use of electrically conductive wires woven into the brush to carry away the static charge.
Brushes, per se, have many drawbacks for applications where it is necessary to prevent any scratching of the plastic surface involved. Such is the case in the photo-processing industry. With the use of even fine brushes made from animal hair, extreme care had to be taken not to scratch the surface of the film. To this end, finer and finer filaments have been developed for use in brushes. These filaments are drawn from plastics such as nylon and acrylic. They-measure only two thousandths of an inch in diameter and have sufficient body and stiffness to be effective in removing the dust and lint from film without scratching it.
Removing the dust from the film does not get rid of the static charge Therefore, brushes have to be augmented with some static eliminating means. The means first used with brushes was a radioactive material of sufficiently low potency so as not to be a health hazard. The material was imbedded in the base of the brush. It was effective in removing the static charge as long as the potency of the radioactivity remained high and the brush was not passed over the film too rapidly. Generally these brushes did not remain effective very long as the radioactive material used, polonium 210, has a half-life of about four and one half months.
Later, specific film cleaners incorporated brushes for removing the dust from the film. A typical design is that presented by Cumming et al, U.S. Pat. No. 4,805,068. In this device, stationary brushes are positioned above and below the film, which contact the film, to remove the dust and lint as the film is pulled between them. Simultaneously, an electrical ionizing means is used to ionize the surrounding air to remove the static charge. Several other devices that incorporate similar designs have been noted on the market.
Metallic brushes have been used to eliminate static charge. One of the earliest designs is that of Gutman, U.S. Pat. No. 2,023,321. This design consists of a tinsel-like garland, formed of metallic elements, stretched across the sheet from which the static was to be removed. Of course, if the metal elements touched a photographic film, they would damage the film. Hence, such a device was never used in photo-processing. Nishikawa, U.S. Pat. No. 4,307,432 uses a brush device made of fine wires (although he doesn't say how fine) to eliminate static charge. However, he positions the brush so that it never contacts the film. This prevents scratching the film, but it also limits the ability to remove static charge. The ability of the charge on the film to discharge to the metal brush wires is relative to the charge on the film and the distance of the wire from the brush. At a distance of only a few thousandths of an inch from the film, the remaining charge that would not be discharged from the film would still be several hundreds or even thousand volts. (My experimental results disagree considerably with Nishikawa's.)
Another brush device presented by Troia, U.S. Pat. No. 3,470,567. Troia uses rotating brushes to clean the film. However, his brushes are spaced from the film so that they make only light intermittent contact with the film as they rotate. The thrust of his invention is to clean the film and still keep the brushes from scratching the film by limiting their contact.
The deficiency of the Nishikawa and Troia technology is that they are concerned with, and treat, two separate aspects that my invention embodies. One removes the static charge and the other removes the dust. It might seem that combining the two would be all that was necessary to remove both. This may be true, but these techniques both have severe limitations and complexities of implementation that are not acceptable in todays present advancements in the state-of-the-art in photo-processing and other related field.